Droppable back-off tool



INVENTOR.

2 Sheets-Sheet 1 Filed Oct. 21, 1955 Nov. 10, 1959 B. H. FUCHS DROPPABLEBACK-OFF TOOL 2 Sheets-Sheet 2 Filed Oct.

INVENTOR. ,gEA/uAMI/V EJ 00462 A'rmm/sy Patented Nov. 10, 3%59 2,911,909DROPPABLE BACK-OFF, TooL Benjamin H. Fuchs, Hollydale, Calif., 'assignorto Emily E. 'Wilcox, Whittier, Caiif.

The invention relates to a back-off tool and more particularly to a toolcarrying an explosive and adapted to be lowered in a drilling string ofpipe, viz., drill pipe, crossover sub, and drill collars, in order toapply an explosive shock at a threaded coupling between such members, tojar the coupling so that torque can be applied to uncouplethe parts.This operation is well known and is usually accomplished by lowering anexplosive, usually a flexible explosive string known as a string shot,into the drill pipe and firing the explosive by a circuit including anelectrical cable connected to the explosive and extending from it to atruck at the ground level. This requires an electrical cable as long asthe distance from the truck to the remote threaded coupling to be jarredloose.

An object of the invention is to avoid the requirement for an electricalor other cable comparable in length to the depth, below the earthssurface, of the coupling to be loosened, and to provide a droppableback-01f tool which can be freely dropped in the drilling string withoutany electrical or other cable attached to it. Hence, the speed ofdropping is determined by theforce of gravity and not by the speed oflowering a cable.

A further object of the invention is to automatically fire an explosivewhen it has reached a desired location determined by a stop located inthe drilling string.

These objects are accomplished by providing a firing circuit which islocal to the back-01f tool, and by controlling this circuit by contactswhich are operated by a stop device which completes the circuit when theex plosive reaches a desired position in the drilling string of pipe.The stop device is arranged beforehand in the drilling string so thatthe explosive will be automatically fired when it reaches the break-awaypoint.

For further details of the invention reference may be made to thedrawings wherein, Figil is a view in elevation, partly in section,showing thetdroppable tool of this invention position in a typicaldrilling string, with a cable used, not for lowering, but only forretrieving the tool.

Fig. 2a and Fig. 2b are enlarged views in elevation, partly in section,of the upper and lower portions respectively of the tool of Fig. l, withthe contacts in open position.

Fig. 3 is an enlarged view in cross section showingthe stop sleeve inposition in the drilling string.

Fig. 4 is a perspective view of the stop sleeve removed from thedrilling string.

Figs. 5a and 5b correspond to Figs. 2a and 2b respectively, showing thetool in firing position with the contacts closed. p

Fig. 6 is a further enlarged sectional view of the tool, with partsbroken away, showing thecontacts open.

Fig. 7 is a sectional view showing a portion of Fig. 6 with the'contactsin firih'g position.

Referring in detail to the drawings, Fig. 1 shows the back-01f tool 1 inposition in a drilling string represented by the drill pipe 2, sub 3,and drill collar 4, con

nected by the usual box thread coupling like 5 and 6. The tool 1comprises an outer hollow cylindrical casing 7 and an inner plunger 8.The plunger 3 at its upper end has a knob 9 having an annular groove 10to receive a latch, not shown, on a sinker-bar 11,'the latter having acable, not shown, to retrieve said tool from the drilling string, ifdesired, after the shot has been fired.

The lower end 12 of the plunger 8 is a string-shot holder and has aspiral groove 13 to receive the flexible explosive or string-shot 14having wires 15 and 16 connected to terminals 17 and 18 respectively.The portion. 19 of plunger 8 above the string-shot holder 12 is ofreduced diameter providing a shoulder 20 which abuts the lower end 271of casing 7 when plunger 8 is in its uppermost position as shown inFigs. 1, 2a, and 2b. The lower end 22 of the casing 7 is of reduceddiameter providing at its upper end a shoulder 23 having a downwardlyfacing bevel, cooperating with the upwardly facing bevel on the upperinner portion of the four fingers like 24 'on a stop sleeve 25. It isknown beforehand where the coupling to be shocked is located, and whilethe shoulder 23 may be located anywhere in the pipe string, by way ofexample, it is assumed that the coupling 6 at the lower end of the sub 3where it joins the upper end of the drill collar 4 is to be shocked.Hence, the stop sleeve 25 is arranged in a counterbore 26 at the upperend of the sub 3, being suitably held in position, e.g., betweenshoulder 26 and the end 27 of pipe 2. A stop serving the same purpose assleeve 25 can be milled as a stop. This locates the string-shot holder12 opposite coupling 6 when stop collar 23 is on stop sleeve 25, ascasing length from collar 23 to its end 21 is of the length thusrequired and in t average case may be about 30 in. long. The tool le isthus determined by the sub length to be backed off.

The upper end of the casing 7 has a spring barrel 30 for a spring 31which urges the plunger 8 upwardly as shown in Fig. 2a, to separate thecontact 32 on the casing, from the contact 33 on the plunger until theweight of the sinker bar 11 and/or the weight of the plunger 8,overcomes the spring 31 to urge the plunger 8 downwardly to the positionshown in Fig. 5a, and close the above-mentioned contacts and fire theshot string 14, this relative movement of plunger 8 and casing '7 beingobtained at the desired location by reason of the fact that the stopsleeve 25 cooperates with the stop collar 23 to determine the point inthe downward travel of the tool 1 through the drilling string where suchrelative movement and hence closure of contacts 32 and 33 shall takeplace.

Spring barrel 3% is in the form of a counter-bore at the end of casing 7and it provides a shoulder 34 for the lower end of this spring. Theupper end of plunger 8 bears against the head 35 having a threadedcoupling 36 with the upper end of plunger 8, and sealed off with agasket 37. v

The upper end of plunger 8 is hollow, providing a batterychamber 449 fora plurality of dry batteries indicated at 41, arranged end to end, thebottom batter-y 42 having a'botto-m terminal connected with a contact 43connected by wire 44 to terminal 18, terminal 17 being grounded on themetal plunger fl. The battery chamber 40 has insulation 45 on its wall.The upper contact of the top battery 41 is connected by a spring 46 to asuitable terminal 47 connected by wire 48 to contact 33, contact 32being grounded on the casing 7. Wires 15 and 16 are connected to a fuse5'43 which detonates the shot-string 14, which may be cordite. v V j Thehead 35 can be removed to replace the batteries 41. The bottom of head35 strikes the top edge 49 of the casing 7 to serve as a stop and limitthe downward movement of the plunger 8 when the casing 7 is stopped bythe stop sleeve 25. The contact 33 is elongated so as to provide awiping connection with contact 32, both when the plunger 8 is goingdownwardly and on its rebound, if any. It is understood that theback-01f tool is dropped in the drilling string free from attachment toanything. After this tool has been used, a new string-shot explosive maybe mounted in the groove 13, and the tool may be used again.

Various modifications may be made in the invention without departingfrom the spirit of the following claims.

I claim:

1. Back-otf apparatus for use in a hollow drilling string including: adroppable back-E tool adapted to be dropped into the hollow drillingstring, said droppable tool including a pair of relatively verticallymovable members, means for carrying an explosive charge on one of saidmembers, a battery circuit in said tool operatively connectable to saidexplosive charge carrying means to detonate said charge upon actuationof said circuit, a pair of normally vertically spaced circuit actuatingmembers, one of which is mounted on each of said relatively movablemembers, at least one of said circuit actuating members beingoperatively connected to said circuit to actuate said circuit when saidcircuit actuating members are operatively engaged, said circuitactuating members being operatively engageable to actuate said circuitupon relative vertical movement of said relatively movable members, anda downwardly directed external shoulder on one of said relativelymovable members; and an upwardly directed shoulder in said hollowdrilling string; whereby said external shoulder carrying member will bestopped upon engagement of said shoulders as said droppable tool dropsthrough said string, the weight and momentum of the other relativelymovable member causing relative vertical movement between the saidrelatively movable members for actuating said circuit and detonatingsaid charge.

2. The apparatus of claim 1 in which said relatively movable members arein telescoping relationship.

3. The apparatus of claim 1 in which spring means operatively engagedbetween said relatively movable members normally urges said relativelymovable members toward a relative vertical position with said circuitactuating members vertically spaced and said circuit unactuated, and inwhich said weight and momentum overcome said spring means to causerelative vertical movement between said members for actuating saidcircuit and detonating said charge.

4. The apparatus of claim 1 in which a stop sleeve is mounted in saidstring to provide said shoulder in said string.

5. Back-off apparatus for use in a hollow drilling string including: adropable back-01f tool adapted to be dropped into the hollow drillingstring, said droppable tool including a hollow casing member, a plungermember vertically slidably mounted in said hollow casing member, meansfor carrying an explosive charge on one of said members, a batterycircuit in said tool operatively connectable to said explosive chargecarrying means to detonate said charge upon actuation of said circuit, apair of normally vertically spaced circuit actuating members, the upperone being mounted on said plunger member and the lower one being mountedon said casing member, at least one of said circuit actuating membersbeing operatively connected to said circuit to actuate said circuit whensaid circuit actuating members are operatively engaged, said circuitactuating members being operatively engageable to actuate said circuitupon downward movement of said plunger member relative to said casingmember, and a downwardly directed external shoulder on said casingmember; and an upwardly directed shoulder in said hollow drillingstn'ng; whereby said casing member will be stopped upon engagement ofsaid shoulders as said droppable tool drops through said string, theweight and momentum of said plunger member causing downward movement ofsaid plunger member relative to said casing member for actuating saidcircuit and detonating said charge.

6. The apparatus of claim 5 in which spring means operatively engagedbetween said casing and plunger members normally urges said plungermember upwardly relative to said casing member to a position whereinsaid circuit actuating members are vertically spaced and said circuit isunactuated, and in which said weight and momentum of said plunger memberovercome said spring means when said casing member is stopped byengagement of said shoulders to cause downward movement of said plungermember relative to said casing member for actuating said circuit anddetonating said charge.

7. The apparatus of claim 5 in which said explosive charge carryingmeans is a string shot holder forming a part of said plunger member.

8. The apparatus of claim 5 in which said explosive charge carryingmeans is located on said plunger and in which battery containing meansfor said battery circuit is provided in said plunger, and in which aportion of said circuit is carried in each of said casing and plungermembers with said circuit actuating members connecting together thesecircuit portions in their respective casing and plunger members whensaid circuit actuating members become operatively engaged upon saiddownward movement of said plunger member relative to said casing member.

9. Back-off apparatus for use in a hollow drilling string, including: adropable back-0E tool adapted to be dropped into the hollow drillingstring, said droppable tool including: a hollow casing, a plungerslidably mounted in said casing and extending both above and below saidcasing, a string shot holder on said plunger below said casing, batterycontaining means mounted in said plunger above said casing, anelectrical conatct on said casing and a cooperating electrical contacton said plunger, a circuit between said battery containing means andsaid holder controlled by said contacts, and a downwardly directedexternal shoulder on said casing; and an upwardly directed shoulder insaid string; whereby said casing will be stopped upon engagement of saidshoulders as said tool drops through said string, the weight andmomentum of said plunger causing downward movement of said plunger insaid casing to bring said contacts into operative engagement with eachother to electrically connect said battery containing means and saidholder.

10. The apparatus of claim 9 in which spring means operatively engagedbetween said casing and said plunger normally urges said plungerupwardly relative to said casing to a position in said casing in whichsaid contacts are out of operative engagement, and in which said weightand momentum of said plunger overcomes said spring means to causedownward movement of said plunger in said casing to bring said contactsinto operative engagement with each other to electrically connect saidbattery containing means and said holder.

11. The apparatus of claim 9 in which a stop sleeve is mounted in saidstring to provide said shoulder in said string.

References Cited in the file of this patent UNITED STATES PATENTS1,623,475 Hammond Apr. 5, 1927 2,427,377 Zschokke Sept. 16, 19472,595,615 Sweetman May 6, 1952 2,620,029 Turechek et al Dec. 2, 19522,621,895 Toelke Dec. 16, 1952 2,705,920 Kanady Apr. 12, 1955 2,745,345Sweetman May 15, 1956

